Antigravity Lifting Gas
An intriguing science-fantasy idea is the existence of antigravity gas -
i.e. a gas which is repelled from, instead of attracted to, massive
bodies by gravity.
The simplest way to work with this is to assume that the gas has a
negative mass. Such a gas would produce greater lift if more of
it is used, so if your gas cells are of a given size, there is an advantage
in compressing it and using very high pressures. It also provides lift by the
buoyancy effect, since it is displacing an equal volume of air. For
greatest buoyancy, you want as large a gasbag as practical.
The following gives an idea of what sort of gas pressure are likely
to be feasible at various Tech Levels:
As I said earlier: these are guesstimates. Any structural engineers out
there are welcome to amend these figures.
- You're looking at gasbags made of animal skin or sailcloth or
something similar, perhaps coated with tar or resin to make it gastight.
Either way, this material is not going to hold much of a pressure
difference before ripping. Maybe 1.1 or 1.2 atmospheres if you're lucky.
- The era of Real World(tm) zeppelins. These had gastight bags with
1 atmosphere of hydrogen. However, I suspect at that TL they could have
coped with an overpressure up to about 1.5 atmospheres, by using metal
banding around the gasbags to keep the stressed bag areas small and so
- You're looking at fully enclosed metal gas containers here.
Titanium or an aluminium alloy would be the choice for lightness and
strength. Strength will depend on the thickness of the metal. You might
reasonably get up to the 2-3 atmospheres mark with a fairly thin sheet
(think aluminium drink can or a bit thicker), but this will be quite
fragile and easy to rupture. Go to centimetre or so thickness of metal
and you're probably talking 10s of atmospheres, maybe up to 100. Of
course the problem then is the weight of the metal itself - though
with enough overpressure of antigravity gas, you'll more than compensate
- Late TL7:
- Advanced structural cloths make an appearance (kevlar, etc).
These can probably get up to the holding strength of thin metal - a
- Structural cloths will get stronger and lighter. You might have
a cloth gasbag capable of holding 10-20 atmospheres.
- Further improvements in materials mean lighter gasbags capable
of holding ever more pressure... perhaps 100 or more atmospheres.
- Force fields become the containment method of choice. For the
weight of a power source and force field generator, you can contain
almost arbitrary levels of pressure. If you use the GURPS Vehicles
"crush depth" rules to determine how much DR you need to withstand a
given pressure difference (A calculation I do not fully agree with...
see Vacuum Lifting Cells) then it comes out to
roughly DR1 per atmosphere. So DR1000 of force field could hold about
1000 atmospheres of overpressure.
Some of this material is based on posts to the Usenet newsgroup
rec.games.frp.gurps by Juergen Hubert.
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